“Please stop fiddling with that and drive,” Jan snaps.

“My car, my dial,” says Serena, and twists it down. The blaring advertisements echoing through the downtown canyon crackle and fade.

Jan shakes his head. “Broad-spectrum antiharmonics. That just makes them breed new frequencies, you know.”

“And my triclosan hand soap created SARS, sure,” says Serena. “You can stay ahead if you’re willing to pay for it. And for this–” she closes her eyes and inhales the silence. “I’m willing.”

“Might be paying more than you think,” sighs Jan.

Behind them, the ambutank roars up, siren on high, silent as surprise.